netconsole prefixes every message

Question

I just enabled netconsole on my Ubiquiti wireless LAN access points. They run a custom OpenWRT or LEDE version, based on Linux Kernel 3.3.8. It works, but the message it sends always contains an additional prefix. While dmesg reads

[   73.690000] netconsole: remote port 6666

it is sent as

{d865 e557} [   73.690000] netconsole: remote port 6666

I confirmed this with wireshark, and using netcat as the receiver. It always contains a prefix consisting of {hhhh hhhh} where h is a lowercase hex digit. The second block always seems to be e557, no matter what device sent the message, while the first block seems to change from time to time, but it does not seem to be related the the facility, time, or severity.

Some samples:

{32f8 e557} [ 2107.350000] br0: port 2(ath0) entered disabled state
{32f8 e557} [ 2109.200000] Restarting system.
{d865 e557} [   73.690000] netconsole: local port 514
{d865 e557} [   73.690000] netconsole: local IP 10.1.0.10
{6d77 e557} [ 1215.920000] STOPPED EVENT for vap 1 (80f50000)

Unfortunately, this build does not have /dev/kmsg so testing is quite uncomfortable.

What is the meaning of this prefix?

Answer 1

Unfortunately, this was due to a patched version of driver/net/netconsole.c. The first four hex characters are a session, that gets randomized during the loading of the netconsole kernel module. The second four hex characters are an internal model number of the AP. You can also get it by running cat /proc/ubnthal/board | grep boardid on the AP.

To get the GPL tarball, you have to contact the support and wait for ages. And I also don't see any copy of the GPL packed with their APs.